Radiation detector probe

ABSTRACT

Tympanic temperature measurements are obtained from the output of a radiation sensor mounted in an extension from a housing. The housing has a temperature display and supports electronics for responding to sensed radiation. The sensor is mounted in an improved extension which is shaped to fit into smaller ear canals, such as a child&#39;s ear canal or a swollen adult ear canal. Within the extension, the sensor is positioned in a highly conductive environment and receives radiation from an external target through a tube. Electronics determine the target temperature based on the sensor output signal and a temperature sensor signal.

RELATED APPLICATION(S)

This application is a continuation of Ser. No. 08/682,260 filed Jul. 17,1996, now U.S. Pat. No. 6,047,205, which is a Continuation of Ser. No.08/333,205, filed Nov. 2, 1994, now U.S. Pat. No. 5,653,238, which is aContinuation-in-part of application Ser. No. 07/832,109, filed Feb. 6,1992, now U.S. Pat. No. 5,325,863 and of application Ser. No.07/889,052, filed May 22, 1992, now U.S. Pat. No. 5,381,796 and ofapplication Ser. No. 07/760,006, filed Sep. 13, 1991, now U.S. Pat. No.5,445,158, which is a Continuation-in-part of application Ser. No.07/646,855, filed Jan. 28, 1991, now U.S. Pat. No. 5,199,436, which is aDivisional of application Ser. No. 07/338,968 filed Apr. 14, 1989, nowU.S. Pat. No. 5,012,813, which is a Continuation-in-part of applicationSer. No. 07/280,546 filed Dec. 6, 1988, now U.S. Pat. No. 4,993,419, theentire teachings of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Radiation detectors which utilize thermopiles to detect the heat fluxfrom target surfaces have been used in various applications. Anindication of the temperature of a target surface may be provided as afunction of the measured heat flux. One such application is the testingof electrical equipment. Another application has been in the scanning ofcutaneous tissue to locate injured subcutaneous regions. An injuryresults in increased blood flow which in turn results in a highersurface temperature. Yet another application is that of ear temperaturemeasurement. More specifically, a tympanic device relies on ameasurement of the temperature of the tympanic membrane area in the earof an animal or human by detection of infrared radiation as analternative to traditional sublingual thermometers. Other eartemperature measurements may be limited to the outer region of the earcanal.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, a radiation detectorcomprises a radiation sensor such as a thermopile and a thermal massenclosing the thermopile. The thermal mass includes an elongatedthermally conductive tube of a first internal diameter. The tube extendsfrom the distal end of the detector to a rear volume of larger internaldiameter in which the sensor is mounted. In one device, the tube is goldplated and is thus highly reflective. In another device the tube isplated with a metal oxide for high absorption of radiation. A rigidwindow is mounted adjacent to an end of the tube, preferably the distalend where it seals the tube.

In accordance with one feature of the present invention, the portions ofthe thermal mass forming the tube and rear volume are formed in aunitary structure of high thermal conductivity material. The unitarythermal structure has an outer surface with an outer diameter at itsdistal end which is less than an outer diameter about the rear volume.The outer surface is tapered about the tube such that a unitary thermalmass of increasing outer diameter is provided about the end of the tubeadjacent to the rear volume. The unitary thermal mass maximizesconductance and thermal mass within a limited diameter. To avoid changesin fixtures used in mounting the thermopile within the unitary thermalstructure, in one embodiment the thermal structure is of limiteddiameter and may be supplemented with an additional thermal mass. Theadditional thermal mass surrounds the rear volume and a portion of thetube and is in close thermal contact with the unitary thermal structure.In another embodiment, the unitary thermal structure extends from thedistal end of the detector to a housing such that no additional thermalmass is required.

It has been found that a narrow field of view radiation detectorprovides a more accurate and reliable reading of tympanic temperature.In the detector of the present invention, that field of view is obtainedby controlling the reflectance of the inner surface of the tube, thelength and diameter of the tube and the position of the thermopilebehind the tube. In one embodiment, the tube has a reflective innersurface providing a field of view from the thermopile of about sixtydegrees or less. A field of view of less than about sixty degrees allowsfor viewing of only a portion of the ear canal within less than about 1centimeter of the tympanic membrane. In another embodiment, the tube hasa nonreflective inner surface which produces a field of view from thethermopile of about thirty degrees or less. In either embodiment, thethermopile response may be fine tuned by changing the position of thethermopile behind the tube which changes the field of view and altersthe thermopile response signal level.

In accordance with another aspect of the present invention, the infraredradiation sensor is mounted in the rear volume within the unitarythermal mass. The sensor has an active area influenced by radiation froman external target and a reference area of known temperature which issubstantially unaffected by radiation. The sensor is preferably athermopile having its cold junction reference area thermally coupled tothe thermal mass but it may be a pyroelectric device. The thermallyconductive tube is thermally coupled to the thermal mass and passesradiation to the sensor from the external target. A thermal barriersurrounds the thermal mass and tube. The temperature of the thermalmass, and thus of the sensor reference area, is allowed to float withambient. A temperature measurement of the thermal mass is made tocompensate the sensor output.

Temperature differences between the tube and sensor reference area wouldlead to inaccurate readings. To avoid those differences, the largeunitary thermal mass minimizes temperature changes from heat whichpasses through the thermal barrier, and good conductivity within themass increases conductance and minimizes temperature gradients. Theouter thermal RC time constant for thermal conduction through thethermal barrier to the thermal mass and tube is at least two, andpreferably at least three orders of magnitude greater than the innerthermal RC time constant for the temperature response of the referencearea to heat transferred to the tube and thermal mass. For promptreadings, the inner RC time constant should be about ½ second or less.

Preferably, the thermally conductive tube is thermally coupled to thesensor by a thermally conductive material such as epoxy. In accordancewith the present invention, the amount of thermally conductive materialis tuned to the detector to minimize the response of the sensor toundesired thermal perturbations of the tube. Providing an insufficientamount of material causes a positive error response from the sensor forthermal perturbations, while too much material causes a negative errorresponse from the sensor for thermal perturbations. By providing theproper amount of material between the sensor and the tube, the addedthermal conductance from the material tunes the reference area and theactive area of the sensor to respond in phase to thermal perturbationssuch that the sensor response is substantially unaffected by saidperturbations.

In the radiation detector of the present invention, the radiation sensorand the tube are positioned in an extension which is particularly suitedfor obtaining tympanic temperature measurements. To accomplish this, theextension is inserted into a subject's ear, and preferably into the earcanal. Once inserted, the extension is pivoted and the sensor scans theear canal and senses the emitted radiation. The detector employselectronics which detects the peak radiation sensed by the sensor andconverts it to a tympanic temperature indication.

The probe extension which supports the radiation sensor extends from ahousing which displays the tympanic temperature. The housing extendsalong a first axis and the extension preferably extends at an angle ofabout 75 degrees from the first axis. This housing supports the batterypowered electronics for converting radiation sensed by the sensor totympanic temperature displayed by the display. The electronics includeda processor for providing the displayed temperature based on radiationreceived from the tympanic membrane. If the sensor receives radiationfrom the cooler outer ear instead of the tympanic membrane, theprocessor determines the displayed temperature as a function of thereceived radiation compensated by an indication of ambient temperatureto produce a core temperature approximation. The entire instrument ishoused in a single hand-held package. The small additional weight of theelectronics in the hand-held unit is acceptable because readings can bemade quickly.

In accordance with another aspect of the present invention, the probeextension is adapted to be inserted into an ear canal. Morespecifically, the diameter of the distal tip as well as the shape andtaper of the extension may be set to provide a detector useful in normaladult ear canals or a pediatric detector useful in small ear canals,especially children's ear canals, and swollen adult ear canals. To thatend, the extension has a diameter of about 3-8 mm about its distal endand a substantially conical shape increasing in diameter along itslength from its distal end and characterized by an included angle ofabout 25-60 degrees. As such, the extension is capable of being insertedinto an ear canal up to one-third of the length of the ear canal.

In a pediatric detector embodiment the conical shape of the extensionhas an included angle of about forty degrees. Further, the diameter ofthe tip of the distal end of the extension is preferably in the range of3-6 min. As such, the pediatric detector is particularly useful onsubjects having small ear canals but is also useful on adult subjects.In another embodiment the conical portion of the extension has anincluded angle of about thirty degrees. The diameter of the tip of thedistal end of the extension is no more than about 7 min. As such, thedetector is particularly useful on adult subjects having normal earcanals, but it may also be used on children.

The radiation sensor assembly of a preferred embodiment includes asensing device which is mounted within a rigid structure of high thermalconductivity such as beryllium oxide and has its reference areathermally coupled thereto. The passage through a thermally conductivetube passes thermal radiation from the external target, such as atympanic membrane, to the thermopile. A window is mounted on the rigidstructure such that it is in close thermal contact with the structure.

In one embodiment of the present invention, a detector comprises asubstantially conical extension employing the above-described radiationsensor assembly. Preferably, the sensor assembly includes a thermopilesensor. In this embodiment, the tube provides a field of view from thethermopile of about thirty degrees or less. A thermal mass of highthermal conductivity material surrounds the tube and encloses the rigidstructure in a rear volume. The thermal mass has a region within therear volume which is defined between a rearwardly facing surface of thethermal mass and forward a face of the window. The region is preferablyfilled with air, providing a low thermal conductivity environmenttherein. The high thermal conductivity mass provides close thermalcontact among the tube, the rigid structure, the thermopile coldjunction and the ends of the window. As such, a continuous low thermalresistance path is formed from the tube to the cold junction of thethermopile and the window is held to the cold junction temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 illustrates one embodiment of a radiation detector for tympanictemperature measurements in accordance with the present invention.

FIG. 2 is a cross-sectional view of the extension of the detector ofFIG. 1 in which the thermopile radiation sensor is positioned.

FIG. 3 illustrates another embodiment of the radiation detector fortympanic temperature measurements in accordance with the presentinvention.

FIG. 4 is a cross-sectional view of the extension of the detector ofFIG. 3 in which the thermopile radiation sensor is positioned.

FIG. 5 is a profile of pair of configurations of the extension of FIG.4.

FIG. 6 is an enlarged cross-sectional view of the extension of FIG. 4.

FIG. 7 is a cross-sectional view of a radiation sensor assembly of thedetector of FIG. 6.

FIG. 8 is a block diagram of the electronic circuit of the detector ofthe present invention.

FIGS. 9A-9D are flow charts of the system firmware.

FIG. 10 is a cross-sectional view of a thermopile can embodying afeature of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In one embodiment of the present invention, the radiation detector 12 ofFIG. 1 includes a flat housing 14 with a digital display 16 fordisplaying a tympanic temperature measurement. Although the display maybe located anywhere on the housing, it is preferred that it bepositioned on the end so the user is not inclined to watch it during ameasurement. The instrument makes an accurate measurement when pivotedto scan the ear canal, and the user should concentrate on only thescanning motion. Then the display can be read. A thermopile radiationsensor is supported within a probe 18 at the opposite end of the housing14. The housing extends along a first axis 19 (FIG. 2) and the extension18 extends orthogonally from an intermediate extension 20 which extendsat an angle of about 15 degrees from the first axis. As such, theextension 18 extends at an angle of about 75 degrees from the first axis19 of the housing. Thus, the head of the detector, including theextension 18 and 20 has the appearance of a conventional otoscope. Anon/off switch 22 is positioned on the housing.

A cross-sectional view of the extension of the detector of FIG. 1 isillustrated in FIG. 2. A base portion 23 is positioned within thehousing 14, and the housing clamps about a groove 24. As noted, theportion 20 extends at about a 15 degree angle from the first axis 19 andthus from the base portion 23. Further, the extension 18 extends atabout a 75 degree angle from the first axis. The extension 18 is taperedtoward its distal end at 26 so that it may be comfortably positioned inthe ear canal to view the tympanic membrane and/or ear canal.

A preferred disposable element to be used over the extension 18 ispresented in the '419 patent and will not be discussed here.

The edge at the end of the probe is rounded so that when the probe isinserted into the ear it can be pivoted somewhat without discomfort tothe patient. The probe is also curved like an otoscope to avoidinterference with the ear. By thus pivoting the probe, the ear canal isscanned and, at some orientation of the probe during that scan, one canbe assured that the maximum temperature is viewed. Since the ear canalcavity leading to the tympanic area is the area of highest temperature,the instrument is set in a peak detection mode, and the peak detectedduring the scan is taken as the tympanic temperature.

An improved assembly within the extension 18 is illustrated in FIG. 2. Athermopile 28 is positioned within a can 30 of high conductivitymaterial such as copper. The conductivity should be greater than twowatts per centimeter per degree Kelvin. The can is filled with a gas oflow thermal conductivity such as Xenon. The thermopile 28 is positionedwithin a rear volume 31. It is mounted to an assembly which includes aheader 33. The volume is sealed by cold welding of the header 33 to aflange 42 extending from the can. Cold welding is the preferred approachto making the seal and, to utilize past welding fixtures, the outerdiameter of the can is limited. Thermal epoxy may be used as analternative.

The thermopile views the tympanic membrane area through a radiationguide 32. The radiation guide 32 is gold plated to minimize oxidation.It is closed at its forward end by a germanium window 35. The rigidgermanium window assures that the radiation guide is sealed fromcontamination and is itself easily cleaned. Germanium is less fragilethan silicon and passes higher wavelengths. To minimize expense, thewindow is square with each side slightly longer than the diameter of theradiation guide 32. The window is cemented with epoxy within acounterbore in a flange 37 at the end of the radiation guide. The epoxyserves as a gas seal and mechanical support for the somewhat brittlegermanium window. The flange serves to protect the germanium windowshould the detector be dropped. The diagonal of the window is less thanthe diameter of the counterbore, and its thickness is less than thedepth of the counterbore. Therefore, if the detector is dropped, anyforce which presses the plastic housing toward the window is absorbed bythe flange. The germanium need only withstand the forces due to its owninertia.

From the perspective of the thermopile flake 28, the radiation guide 32shifts the front aperture at the window 35 back to the proximal end ofthe radiation guide at 46. Thus, the field of view of the device isdetermined by the diameter of the aperture 46 and its distance from theflake 28. There are, however, stray rays which, though not beingdirected to the flake from the aperture, may ultimately strike the flakeafter reflection within the volume at 31. Such reflections effectivelyincrease the field of view and are thus undesirable. The frustoconicalsurface 44 surrounding the aperture 46 reflects most of those stray raystoward the rear of the volume 31 rather than toward the thermopileflake. As shown in FIG. 2, the flake views itself in the surface 44,thus minimizing stray radiation.

The angled surface surrounding the aperture can be applied to moreconventional thermopile cans as illustrated in FIG. 10. Here, the window310 is mounted directly across the aperture 312 of the can 314. As inconventional assemblies, the can is closed by rear header 316. Thethermopile flake 318 is centered on a polyester sheet 320 stretchedbetween beryllium oxide rings 322 and 324. As in the case of FIG. 2, thesurface 326 surrounding the aperture 312 is frustoconical such that itis angled back from the aperture. It can be seen that stray rays 328which should not be seen by the thermopile flake 318 will be reflectedrearwardly toward the beryllium oxide rings where they should beabsorbed rather than toward the flake as indicated by the broken linesas they would if the surface surrounding the aperture were cylindrical.

Whereas the detector disclosed in the '419 patent had a field of view ofabout 120°, it has been determined that a narrower field of view ofabout sixty degrees or less provides the user with an easier and moreaccurate indication of tympanic temperature. With a narrower field ofview, the thermopile flake, when directly viewing the tympanic membrane,also views less than about one centimeter along the ear canal whereinthe tissue is at substantially the same temperature as the tympanicmembrane. A better view of the tympanic membrane also results from thecylindrical extension 43 beyond the conical portion of the extension 18.With the ear canal straightened by the probe, the extension 43 canextend well into the ear canal beyond any hair at the canal opening.

The tympanic membrane is about 2.5 centimeters from the opening of theear canal. The ear canal for an adult subject is typically about 8 mmwide, so the diameter of the tip of the extension is no more than about8 mm wide. The conical portion of the extension 18 prevents the tip ofthe extension from extending more than about eight millimeters into theear canal. Beyond that depth, the patient suffers noticeable discomfort.With a field of view of less than about sixty degrees, the ear canal isviewed more than about eight millimeters from the tip of the extension18. Thus, only the ear canal within less than 9 millimeters of thetympanic membrane is viewed as the radiation guide is directed towardthe membrane. The result is a more accurate and reliable reading of thetympanic temperature which is essentially core temperature.

With the present instrument, the narrow field of view is obtained byextending the enlarged rear volume between the flake and the radiationguide. Radiation which enters the radiation guide at greater angles, yettravels through the radiation guide, leaves the guide at greater anglesand is thus unlikely to be viewed by the flake. The length of theradiation guide is another parameter which affects the field of view. Byusing a planoconvex lens as the window 35, the field of view can befurther limited.

Decreasing the field of view increases the amount of heat which isabsorbed by the can in which the thermopile is mounted. The added heatload adds to the importance that the can, including the radiation guide,have a large thermal mass and high thermal conductivity as discussedbelow.

As distinguished from the structure presented in the '419 patent, thevolume 31 surrounding the thermopile and the radiation guide are formedof a single piece of high conductivity copper. This unitary constructioneliminates any thermal barriers between the foremost end of theradiation guide and the portion of the can surrounding the thermopilewhich serves as the cold junction of the thermopile. Further, at least aportion of added thermal mass which surrounds the radiation guide isunitary with the can as well. Specifically, a taper 39 results in anenlarged region 41 which serves as a thermal mass in accordance with theprincipals of the parent application. The taper 39 continues along aconductive thermal mass 34 which surrounds the can and a conductive plug36. Both the mass 34 and plug 36 are of copper and are in close thermalcontact with the can 30.

The outer sleeve 38 of the extension 18 and the intermediate extension20 are of plastic material of low thermal conductivity. The sleeve 38 isseparated from the can 30 and thermal mass 34 by an insulating air space40. The taper of the can 30 and thermal mass 34 permits the insulatingspace to the end of the extension while minimizing the thermalresistance from the end of the tube 32 to the thermopile, a parameterdiscussed in detail below. The inner surface of the plastic sleeve 38may be coated with a good thermal conductor to distribute across theentire sleeve any heat received from contact with the ear. Twenty milsof copper coating would be suitable.

In contrast with the prior design, the portion of the sleeve 38 at theforemost end of extension 18 has a region 43 of constant outer diameterbefore a tapered region 45. The region of constant outer diameterreduces the outer diameter at the distal end and minimizes interferencewhen pivoting the extension in the ear to view the tympanic membranearea. The tapered region is spaced six millimeters from the end of theextension to allow penetration of the extension into the ear canal by nomore than about eight millimeters.

One of the design goals of the device was that it always be in propercalibration without requiring a warm-up time. This precluded the use ofa heated target in a chopper unit or heating of the cold junction of thethermopile as was suggested in the O'Hara et al. U.S. Pat. No.4,602,642. To accomplish this design goal, it is necessary that thesystem be able to operate with the thermopile at any of a wide range ofambient temperatures and that the thermopile output have very lowsensitivity to any thermal perturbations.

The output of the thermopile is a function of the difference intemperature between its warm junction, heated by radiation, and its coldjunction which is in close thermal contact with the can 30. In orderthat the hot junction respond only to radiation viewed through thewindow 35, it is important that the radiation guide 32 be, throughout ameasurement, at the same temperature as the cold junction. To that end,changes in temperature in the guide 32 must be held to a minimum, andany such changes should be distributed rapidly to the cold junction toavoid any thermal gradients. To minimize temperature changes, the tube32 and the can 30 are, of course, well insulated by means of the volumeof air 40. Further, a high conductance thermal path is provided to thecold junction. This conductance is enhanced by the unitary construction.Further, the can 30 is in close thermal communication with the thermalmasses 34 and 36, and the high conductivity and thickness of the thermalmasses increase the thermal conductance. A high thermal conductivityepoxy, solder or the like joins the can and thermal masses. The solderor epoxy provides a significant reduction in thermal resistance. Wheresolder is used, to avoid damage to the thermopile which is rated totemperatures of 125° C., a low temperature solder of indium-tin alloywhich flows at 100° C. is allowed to flow into the annular mass 34 toprovide good thermal coupling between all elements.

The thermal resistance from the outer surface of the plastic sleeve 38to the conductive thermal mass is high to minimize thermal perturbationsto the inner thermal mass. To minimize changes in temperature of theguide 32 with any heat transfer to the can which does occur, the thermalmass of the can 30, annular mass 34 and plug 36 should be large. Tominimize thermal gradients where there is some temperature change in thetube during measurement, the thermal resistance between any two pointsof the thermal mass should be low.

Thus, due to the large time constant of the thermal barrier, anyexternal thermal disturbances, such as when the extension contacts skin,only reach the conductive thermal mass at extremely low levels during ameasurement period of a few seconds; due to the large thermal mass ofthe material in contact with the cold junction, any such heat transferonly causes small changes in temperature; and due to the good thermalconductance throughout the thermal mass, any changes in temperature aredistributed quickly and are reflected in the cold junction temperaturequickly so that they do not affect temperature readings.

The thermal RC time constant for thermal conduction through the thermalbarrier to the thermal mass and tube should be at least two orders ofmagnitude greater than the thermal RC time constant for the temperatureresponse of the cold junction to heat transferred to the tube andthermal mass. The RC time constant for conduction through the thermalbarrier is made large by the large thermal resistance through thethermal barrier and by the large thermal capacitance of the thermalmass. The RC time constant for response of the cold junction is made lowby the low resistance path to the cold junction through the highlyconductive copper can and thermal mass, and the low thermal capacitanceof the stack of beryllium oxide rings and pin conductors to thethermopile.

Although the cold junction capacitance is naturally low, there are sizeconstraints in optimizing the thermal capacitance of the thermal mass,the thermal resistance through the thermal barrier and the internalthermal resistance. Specifically, the external thermal resistance can beincreased by increased radial dimensions, the capacitance of the thermalmass can be increased by increasing its size, and the thermal resistancethrough the longitudinal thermal path through the tube can be decreasedby increasing its size. On the other hand, the size must be limited topermit the extension to be readily positioned and manipulated within theear.

Besides the transfer of heat from the environment, another significantheat flow path to the conductive thermal mass is through leads to thesystem. To minimize heat transfer through that path, the leads are keptto small diameters. Further, they are embedded in the plug 36 throughbores 70; thus, any heat brought into the system through those leads isquickly distributed throughout the thermal mass, and only small changesin temperature and small gradients result.

Because the temperature of the thermal mass is not controlled, and theresponse of the thermopile 28 is a function of its cold junctiontemperature, the cold junction temperature must be monitored. To thatend, a thermistor is positioned at the end of a central bore 72 in theplug 36.

Another embodiment of the present invention is illustrated in FIG. 3.The radiation detector 212 employs a thermopile radiation sensorsupported within a probe extension 218 of the opposite end of thehousing 14. As shown in FIG. 4, the extension 218 extends at an angle ofabout 75 degrees from a first axis 219 along which the housing extends.The extension 218 is tapered along its length from its distal end,making the instrument 212 particularly useful in obtaining tympanictemperature measurements without causing the subject discomfort.

As previously discussed, the other embodiment provided an extension witha constant diameter tip which works well in ear canals of about the samediameter. However, this tip does not fit within smaller ear canals, andsubjects with larger diameter ear canals will suffer discomfort as theconstant diameter tip of the extension contacts the walls of their earcanals during pivoting to scan the ear canal. In accordance with thepresent invention, the substantially conical shaped extension 218 has anincreasing diameter along a portion of its length from its distal endsuch that the extension may be inserted into an ear canal withoutcausing discomfort. Once inserted, the extension 218 is pivoted to scanthe ear canal adjacent to and including the tympanic membrane. Theconical shape of the extension 218 ensures that the edge of the tip ofthe extension is unable to contact the walls of the ear canal. Thethermopile 28 senses radiation within the ear canal during the pivotalrotation of the extension 218. The detector 212 employs electronics inthe housing 14 for detecting the peak radiation sensed by the sensor 28and converting it to a tympanic temperature indication. Further, theelectronics may also provide an audible tone indicating that peakradiation has been detected for a particular measurement period. Thevariable tone or variable pulse signal allows a user to know when tostop pivoting the extension for a given subject.

The diameter of the distal tip of the probe extension as well as itstaper may be selected to provide a detector useful in normal ear canalsor a pediatric detector useful in small ear canals. In oneconfiguration, as shown in FIG. 5, the extension 218 has a smalldiameter tip and is tapered along its length at its distal end makingthe extension particularly suited for insertion into small ear canals. Asmall ear canal is about 3-6 mm wide, so the diameter of the extension218 along the portion of its length from its distal tip 226 is no morethan about 3-6 mm. Further, the extension 218 comprises an outer sleeve238 with a tapered portion 245 extending at a twenty degree angle fromthe distal tip 226. As such, the conical portion 245 of the extensionhas an included angle of about forty degrees. With a preferred 3.4 mmouter diameter at the tip 226 and a forty degree included angle alongthe conical portion 245, the extension 218 is capable of being insertedabout 4 mm into a small ear canal. A young child's ear canal is about 10mm in length, so the extension may be inserted into the child's earcanal up to about one-third of the length of the ear canal withoutcausing discomfort.

In another configuration, indicated by dashed lines in FIG. 5, anextension 318 has a larger diameter tip and is tapered such that theextension is particularly suited for normal ear canals including adultear canals and ear canals of older children. A normal ear canal is about8 mm wide, and the diameter of the extension 318 about its distal tip326 is no more than 7 mm. The tapered portion 345 of the outer sleeveextends at about a fifteen degree angle from the distal tip 326 whichcorresponds to a thirty degree included angle. As such, the extension318 having a preferred tip diameter of about 5 mm is capable of beinginserted about 8 mm into a normal ear canal, or about one-third of thelength into the canal without causing the subject discomfort.

Referring to FIG. 5, the extensions 218 and 318 have different profileswhich were selected to minimize discomfort to the subject and to providefor accurate tympanic temperature readings. To that end, the diameter ofthe tip of the extensions is specified and depends on the diameter ofthe subject's ear canal. Further, the extensions are configured toprovide a field of view of about thirty degrees which provides moreaccurate readings as explained below. Thus, to provide a thirty degreefield of view at θ₁, with a 3 mm inner diameter of tube 232, the length21 from the tip 226 to the thermopile 28 is about 7.5 mm. Due to theproximity of the thermopile 28 to the tip (7.5 mm), the extension 218requires the steeper taper of 20 degrees so that the thermopile assembly(not shown) fits into the extension. Also, the taper of 20 degreesprovides a necessary stop in close proximity to the distal end 226 forpreventing insertion of the extension 218 too far into a short ear canalso as to cause discomfort. To achieve the thirty degree field of view atθ₂ with a tube 322 diameter of about 4.5 mm, a length of L2 of about 11mm is required. Due to the larger diameter tip 326, the thermopile 328is further from the tip for the same field of view so that the conicalportion 345 may have a 15 degree taper. An adult canal has a flap ofcartilage at the outer region of the ear (the concha). Thus, the conicalportion 345 having the 15 degree taper is advantageous as it allows theextension 318 to be narrower and thus be inserted past the cartilage andextend into the ear canal.

An improved assembly within the extension 218 is shown in FIG. 4. Athermopile 28 is positioned within a thermal mass 230 formed of highthermal conductivity material such as copper. In contrast to theprevious embodiment, the thermal mass 230 is a one-piece structure whichmounts into a bore 233 within a portion 220 of the extension 218.Further, no contact between the thermal mass 230 and the outer sleeve238 is made at the distal end 226 of the extension. Instead, a ridge 242in the mass 230 contacts the sleeve 238 to achieve alignment of the massand the distal end of the sleeve. The thermopile 28 is located in a rearvolume 231 and views the tympanic membrane area through a conductivetube 232 formed in the mass 230.

Referring to FIGS. 6 and 7, the thermopile is mounted on the rearsurface of a sheet of polytetrafluoroethylene 248 suspended from therear surface of a first beryllium oxide ring 250. A mass of infraredabsorbing black material 258 is positioned on the opposite surface ofthe sheet and serves as a radiation collector. A second beryllium oxidering 252 supports the first ring 250 and the two rings are supported bya copper header 256. A window 235 formed of silicon or germanium ismounted on the first ring 250. The rings 250 and 252, the window 235 andthe header 256 are thermally coupled by high thermal conductivity epoxy255. A pair of leads 260 formed of 20 mils of kovar provide structuralsupport to the assembly and provide a thermopile output signal to theelectronics via a pair of 40 gauge wires 262. As such, the tube and theregion defined by the surface 237 and the window 235 are filled withair. A sufficient amount of silver paint may be included within therings to oxidize all air, and thus create a nitrogen environment in thegas tight region. Alternatively, the window may be positioned at thedistal end 226 of the housing 218 as indicated by the dashed lines inFIG. 4. Having the window positioned directly on the sensor assemblyminimizes temperature gradients between the window and thermopile, butpositioning the window at the distal end minimizes contamination of thesurface of tube 232.

It has been determined that a significantly narrower field of viewprovides the user with an easier and more accurate tympanic temperatureindications. The detector disclosed in the '419 patent had a wide fieldof view of about 120° and the detectors disclosed in the '813 patent anddescribed in the other embodiment have a field of view of about 60° orless. Thus, one object of this embodiment was to reduce the field ofview to obtain a narrower field of view of about thirty degrees or less.To that end, the narrower field of view is obtained by plating the innersurface of the tube 232 with a layer of non-reflective material.Preferably, the non-reflective layer is a metal oxide such as nickeloxide or aluminum oxide. A metal oxide layer is employed because metaloxides are durable and will not change in properties if the innersurface of the tube is cleaned. Further, the metal oxide layer should bethin (a few tenths of thousandths of an inch) such that virtually notemperature gradient exists across the layer. The metal oxide surfaceabsorbs substantially all radiation which strikes the tube 232 andallows radiation passing directly through the tube to reach thethermopile 28.

The dimensions of the tube 232 are chosen such that radiation enteringthe tube at angles of only up to fifteen degrees from the longitudinalaxis of the tube passes directly to the thermopile. With the thirtydegree field of view, the probe can easily be positioned such thatsubstantially only the tympanic membrane may be viewed.

The above approach to decreasing the radiation gathering aperture sizeto about 3 mm and reducing the field of view to about thirty degreessignificantly increases the noise level at the thermopile relative tothe signal level. Further, this approach increases the amount ofradiation which is absorbed by the thermal mass in which the thermopileis mounted. These two effects add to the importance that the thermalmass, including the tube, provide a large thermal mass and high thermalconductivity.

The thermal mass 230 is of unitary construction which eliminates thermalbarriers between the tube 232 and the portion 241 of the thermal masssurrounding the thermopile 28. Further, a plug 272 of high thermalconductivity material positioned behind the thermopile 28 is in closethermal contact with the mass 230. The outer sleeve 238 is formed of lowthermal conductivity plastic and is separated from the mass 230 by aninsulating air space 240. The taper 239 of the mass 230 increases theinsulating air space adjacent to the end of the extension 226 whileminimizing thermal resistance from the tube 232 to the thermopile. Theinner surface of the plastic sleeve 238 may be coated with a goodthermal conductor to distribute across the entire sleeve any heatreceived from contact with the ear.

In order that the hot junction respond only to radiation viewed throughthe window 235, it is important that the tube 232 and the window 235 be,throughout a measurement, at the same temperature as the cold junction.The thermopile 28 acts as a thermal amplifier having a gain based on thenumber of junctions and the Seebeck coefficient. Thus, temperaturegradients sensed by the thermopile are amplified by a factor of about100. To minimize errors, changes in temperature in the tube 232 must beheld to a minimum, and any such changes should be distributed rapidly tothe cold junction to avoid any thermal gradients. To minimizetemperature changes, the tube 232 and the mass 230 are well insulated bymeans of the volume of air 240. To avoid thermal gradients, the tube 232is plated with a thin layer of high conductance non-reflectance metaloxide which minimizes temperature gradients across the layer. Further,the thermal mass 230 is thermally coupled to the rings 250 and 252 withhigh conductivity thermal epoxy 255 such that a high conductance thermalpath is provided from the tube 232 to the cold junction. Thisconductance is enhanced by the unitary construction of the mass 230.

In accordance with another aspect of the invention, the amount ofthermal epoxy 255 between the rings 250 and 252 and the mass 230 istuned to the assembly to minimize the response of the thermopile 28 toundesired thermal perturbations at the end of the mass. Referring toFIG. 6, thermal variations in the air region 243 lead to heating of thetip 227 of the mass 230 which causes the inner surface of the tube 232to emit radiation. If these thermal variations are not sensed by thecold junction via the high conductance thermal path from the tube 232 inphase with the sensing of the radiation by the hot junction, thethermopile 28 produces an error response.

Accordingly, the epoxy 255 may be incrementally added to adjust the highconductivity thermal path to the cold junction to bring the hot and coldjunction thermal responses in phase. An insufficient amount of epoxy 255causes a positive error response as the hot junction responds to thermalvariations faster than the cold junction. Alternatively, too much epoxy255 causes a negative error response as the cold junction respondsfaster to thermal variations than the hot junction. When the properamount of epoxy has been provided, the tuned assembly produces no morethan 0.1° thermopile response for up to 20° thermal variations during atest.

It has been determined in previous devices that a significant source ofthermal gradients is caused by radiation from the window. To minimizethese thermal gradients, the window 235 is mounted on the ring 250 withhigh thermal conductivity epoxy 255 such that it is thermally coupled tothe cold junction. The epoxy provides a significant reduction in thermalresistance and provides good thermal coupling between all elements. Onthe other hand, conductance to the viewing region of the window shouldnot be less than that to the cold junction. Thus, the window 235 isspaced from a rear face 237 of the mass 230 and its ends are spaced fromthe inner volume 231 by a low thermal conductivity air region. Theregion ensures that temperature gradients are distributed to the coldjunction via the thermal mass and not directly through the windowcausing thermal gradients.

The thermal resistance from the outer surface of the plastic sleeve 238to the conductive thermal mass 230 is high to minimize thermalperturbations to the inner thermal mass. The thermal mass is large tominimize changes in temperature of the tube 232 with any heat transferto the mass which does occur. Further, the thermal resistance betweenany two points of the thermal mass 230, the tube 232, the window 235 orthe rings 250 and 252 is low to minimize thermal gradients where thereis some temperature change in the tube during measurement.

Thus, due to the large time constant of the thermal barrier 238, anyexternal thermal disturbances, such as when the extension contacts skin,only reach the conductive thermal mass 230 at extremely low levelsduring a measurement period of a few seconds. Due to the large thermalmass of the materials in contact with the cold junction, any such heattransfer only causes small changes in temperature. Also, due to the goodthermal conductance throughout the thermal mass, tube, window and ringsany changes in temperature are distributed quickly and are reflected inthe cold junction temperature quickly so that they do not affecttemperature readings.

The thermal RC time constant for thermal conduction through the thermalbarrier 238 to the thermal mass 230 and tube 232 is at least two ordersof magnitude greater than the thermal RC time constant for thetemperature response of the cold junction to heat transferred to thetube and thermal mass. The RC time constant for conduction through thethermal barrier 238 is made large by the large thermal resistancethrough the thermal barrier and by the large thermal capacitance of thethermal mass. The RC time constant for response of the cold junction ismade low by the low resistance path to the cold junction through thehighly conductive thermal mass, and the low thermal capacitance of thestack of beryllium oxide rings to the thermopile.

Besides the transfer of heat from the environment, another significantheat flow path in the system is through the leads 260. To minimize heattransfer through that path, the lead diameters are kept small and theleads 260 are trimmed off in the region 246. A pair of 40 gauge wires262 are soldered to the shortened leads 260. The wires 262 extend fromthe region 246 through the plug 272 and provide thermopile signals tothe electronics.

Yet another potential heat flow path in the system is through the header256 to the plug 272. Since the header is in close thermal contact withthe thermopile cold junction, any thermal gradients through the header256 would be amplified 100 to 1000 times by the thermopile producinglarge error signals. In the present invention, the insulating region 246of air is provided behind the header 256 to minimize heat transferthrough that path. Thus, any thermal gradients in the plug would beforced to travel through the mass 230 and would be substantiallydissipated without affecting the thermopile.

Because the temperature of the thermal mass 230 is not controlled andthe response of the thermopile 28 is a function of its cold junctiontemperature, the cold junction temperature must be monitored. To thatend, a thermistor 271 is positioned adjacent to the region 246 in theplug 272. The plug 272 is in thermal contact with the mass 230 such thatthe thermistor 271 is thermally coupled to the cold junction of thethermopile 28. However, the thermal path between the thermopile 28 andthe thermistor has some thermal resistance. This resistance produces atemperature difference between the cold junction temperature and thesensed temperature which is not amplified. Therefore such error is notas significant as gradient errors amplified by the thermopile.

A schematic illustration of the electronics in the housing 14 of bothembodiments of the present invention (FIGS. 1 and 3), for providing atemperature readout on display 16 in response to the signal from thethermopile, is presented in FIG. 8. The system is based on amicroprocessor 73 which processes software routines included in readonly memory within the processor chip. The processor may be a 6805processor sold by Motorola.

The voltage generated across the thermopile 28 due to a temperaturedifferential between the hot and cold junctions is amplified in anoperational amplifier 74. For the detector of FIG. 1, the choppercircuit 67 is not employed and analog output from the amplifier 74 isapplied as one input to a multiplexer 76. For the detector of FIG. 3,the thermopile output voltage is smaller so the amplifier 74 isconfigured in the chopper stabilized amplifier circuit 67. The circuitemploys a switched feedback loop that removes internal offset voltagesassociated with the amplifier 74. The feedback loop comprises switches69 and 71, an amplifier 73 and a storage capacitor C11. When theradiation detector is powered on, switch 69 is opened and switch 71 isclosed. With this configuration, the feedback loop stores the offsetvoltage for the amplifier 74 in capacitor C11. The switch positions arethen reversed such that the input signal to amplifier 74 is combinedwith the offset stored in the capacitor C11. The combined output isapplied an input to the multiplexer 76.

Another input to the multiplexer 76 is a voltage taken from a voltagedivider R1, R2 which is indicative of the potential V+ from the powersupply 78. A third input to the multiplexer 76 is the potential across athermistor RT1 mounted in the bore 72 of block 36. The thermistor RT1 iscoupled in a voltage divider circuit with R3 across a referencepotential VRef. The final input to the multiplexer is a potential takenfrom a potentiometer R4 which may be adjusted by a user. The system maybe programmed to respond to that input in any of a number of way. Inparticular, the potentiometer may be used as a gain control or as a DCoffset control.

At any time during the software routine of the microprocessor 73, one ofthe four inputs may be selected by the select lines 78. The selectedanalog signal is applied to a multiple slope analog system 80 used bythe microprocessor in an integrating analog-to-digital conversion 80.The subsystem 80 may be a TSC500A sold by Teledyne. It utilizes thereference voltage VRef from a reference source 82. The microprocessor 73responds to the output from the converter 80 to generate a countindicative of the analog input to the convertor.

The microprocessor drives four 7-segment LED displays 82 in amultiplexed fashion. Individual displays are selected sequentiallythrough a column driver 84, and within each selected display the sevensegments are controlled through segment drivers 86.

When the switch 22 on the housing is pressed, it closes the circuit fromthe battery 78 through resistors R5 and R6 and diode D1 to ground. Thecapacitor C1 is quickly charged, and field effect transistor T1 isturned on. Through transistor T1, the V+ potential from the storage cell78 is applied to a voltage regulator 86. The regulator 86 provides theregulated +5 volts to the system. It also provides a reset signal to themicroprocessor. The reset signal is low until the +5 volt reference isavailable and thus holds the microprocessor in a reset state. When the+5 volts is available, the reset signal goes high, and themicroprocessor begins its programmed routine.

When the switch 22 is released, it opens its circuit, but a charge ismaintained on capacitor C1 to keep transistor T1 on. Thus, the systemcontinues to operate. However, the capacitor C1 and transistor T1provide a very simple watchdog circuit. Periodically, the microprocessorapplies a signal through driver 84 to the capacitor C1 to recharge thecapacitor and thus keep the transistor T1 on. If the microprocessorshould fail to continue its programmed routine, it fails to charge thecapacitor C1 within a predetermined time during which the charge on C1leaks to a level at which transistor T1 turns off. Thus, themicroprocessor must continue in its programmed routine or the systemshuts down. This prevents spurious readings when the processor is notoperating properly.

With transistor T1 on, the switch 22 can be used as an input throughdiode D2 to the microprocessor to initiate any programmed action of theprocessor.

In addition to the display, the system has a sound output 90 which isdriven through the driver 84 by the microprocessor.

In order to provide an analog output from the detector, adigital-to-analog convertor 92 is provided. When selected by line 94,the convertor converts serial data on line 96 to an analog output madeavailable to a user.

Both calibration and characterization data required for processing bythe microprocessor may be stored in an electrically erasableprogrammable read only memory (EEPROM) 100. The EEPROM may, for example,be a 93c46 sold by International CMOS Technologies, Inc. The data may bestored in the EEPROM by the microprocessor when the EEPROM is selectedby line 102. Once stored in the EEPROM, the data is retained even afterpower down. Thus, though electrically programmable, once programmed theEEPROM serves as a virtually nonvolatile memory.

Prior to shipment, the EEPROM may be programmed through themicroprocessor to store calibration data for calibrating the thermistorand thermopile. Further, characterization data which defines thepersonality of the infrared detector may be stored. For example, thesame electronics hardware, including the microprocessor 73 and itsinternal program, may be used for a tympanic temperature detector inwhich the output is accurate in the target temperature range of about60° F. to a 110° F. or it may be used as an industrial detector in whichthe target temperature range would be from about −100° F. to 5000° F.Further, different modes of operation may be programmed into the system.For example, several different uses of the sound source 90 areavailable.

Proper calibration of the detector is readily determined and the EEPROMis readily programmed by means of an optical communication link whichincludes a transistor T2 associated with the display. A communicationboot may be placed over the end of the detector during acalibration/characterization procedure. A photodiode in the bootgenerates a digitally encoded optical signal which is filtered andapplied to the detector T2 to provide an input to the microprocessor 73.In a reverse direction, the microprocessor may communicate optically toa detector in the boot by flashing specific segments of the digitaldisplay 82. Through that communication link, an outside computer 106 canmonitor the outputs from the thermistor and thermopile and perform acalibration of the devices. A unit to be calibrated is pointed at eachof two black body radiation sources while the microprocessor 73 convertsthe signals and sends the values to the external computer. The computeris provided with the actual black body temperatures and ambienttemperature in the controlled environment of the detector, computescalibration variables and returns those variable to be stored in thedetector EEPROM. Similarly, data which characterizes a particularradiation detector may be communicated to the microprocessor for storagein the EEPROM.

A switch 108 is positioned behind a hole 110 (FIG. 1) in the radiationdetector so that it may be actuated by a rigid metal wire or pin.Through that switch, the user may control some specific mode ofoperation such as converting the detector from degrees Fahrenheit todegrees centigrade. That mode of operation may be stored by themicroprocessor 73 in the EEPROM so that the detector continues tooperate in a specific mode until a change is indicated by closing theswitch 108.

A switch 106 may be provided either internally or through the housing tothe user to set a mode of operation of the detector. By positioning theswitch at either the lock position, the scan position or a neutralposition, any of three modes may be selected. The first mode is thenormal scan mode where the display is updated continuously. A secondmode is a lock mode where the display locks after a selectable delay andthen remains frozen until power is cycled or, optionally, the power-onbutton is pushed. The sound source may be caused to sound at the time oflock. The third mode is the peak mode where the display reads themaximum value found since power-on until power is cycled or, optionally,the power-on button is pushed.

The processor determines when the voltage from the divider R1, R2 dropsbelow each of two thresholds. Below the higher threshold, the processorperiodically enables the sound source to indicate that the battery islow and should be replaced but allows continued readout from thedisplay. Below the lower threshold, the processor determines that anyoutput would be unreliable and no longer displays temperature readings.The unit would then shut down upon release of the power button.

In the present system, the target temperature is computed from therelationship

T _(T) ⁴ =Kh(H−H _(o))+T _(H) ⁴  (1)

where T_(T) is the target temperature, Kh is a gain calibration factor,H is the radiation sensor signal which is offset by H_(o) such that(H−H_(o))=0 when the target is at the cold junction temperature of thedevice to counter any electronic offsets in the system, and T_(H) is thehot junction temperature. This relationship differs from that previouslyused in that Kh is temperature compensated relative to the averagetemperature of the thermopile rather than the cold junction, or ambient,temperature. Further, the hot junction temperature rather than the coldjunction temperature is referenced in the relationship.

The gain calibration factor Kh is temperature compensated by therelationship $\begin{matrix}{{Kh} = {G\left( {1 - {{Tco}\left( {\frac{T_{H} - T_{C}}{2} - {Tz}} \right)}} \right)}} & (2)\end{matrix}$

where G is an empirically determined gain in the system, Tco is thetemperature coefficient of the Seebeck coefficient of the thermopile andTz is the temperature at which the instrument was calibrated. The use ofthe average temperature of the thermopile rather than the cold junctiontemperature provides for a much more accurate response where a targettemperature is significantly different from the ambient temperature.

As noted, the relationship by which the target temperature is determinedincludes the hot junction temperature as the second term rather than thecold junction temperature. Hot junction temperature is computed from therelationship

V _(s) =Jα _(tav)(T _(H) −T _(C))  (3)

where J_(N) is the number of junctions in the thermopile and α_(tav) isthe specified Seebeck coefficient at the average temperature of thethermopile. The Seebeck coefficient can be determined from therelationship $\begin{matrix}{\alpha_{tav} = {\alpha_{ts}\left( {1 - {{Tco}\left( {\frac{T_{H} - T_{C}}{2} - T_{S}} \right)}} \right)}} & (4)\end{matrix}$

where α_(ts) is the specified Seebeck coefficient at a particularspecification temperature and T_(S) is that specification temperature.Again, it can be seen that temperature compensation is based on theaverage thermopile temperature rather than just the cold junctiontemperature. By substituting equation (4) into equation (3) and solvingfor T_(H), the hot junction temperature is found to be

t _(H)=[(Tco*T _(S)+1)±[(Tco*Ts+1)²−(2*Tco)*[(Tco((Tc*Ts)−(Tc²/2))+Tc+(V _(S) /J*α _(ts))]]^(½) ]/Tco  (5)

The actual sensor output V_(s) can be determined from the digital valueavailable to the processor from the equation: $\begin{matrix}{V_{S} = {\left( {H - H_{o}} \right)\frac{K_{AD}}{G_{FE}}}} & (6)\end{matrix}$

where K_(AD) is the analog-to-digital conversion factor in volts/bit andG_(FE) is the gain of the front end amplifier.

Reference to the hot junction temperature rather than the cold junctiontemperature in each term of the relationship for determining the targettemperature provides for much greater accuracy over a wide range ofambient temperatures and/or target temperatures.

To provide a temperature readout, the microprocessor makes the followingcomputations: First the signal from thermistor RT1 is converted totemperature using a linear approximation. Temperature is defined by aset of linear equations

y=M(x−xo)+b

where x is an input and xo is an input end point of a straight lineapproximation. The values of M, xo and b are stored in the EEPROM aftercalibration. Thus, to obtain a temperature reading from the thermistor,the microprocessor determines from the values of xo the line segment inwhich the temperature falls and then performs the computation for ybased on the variables M and b stored in the EEPROM.

The hot junction temperature is computed. A fourth power representationof the hot junction temperature is then obtained by a lookup table inthe processor ROM.

The sensed radiation may be corrected using the gain calibration factorKh, the sensor gain temperature coefficient Tco, the average of the hotand cold junction temperatures and a calibration temperature Tz storedin the EEPROM. The corrected radiation signal and the fourth power ofthe hot junction temperature are summed, and the fourth root is taken.The fourth root calculation is also based on a linear approximationwhich is selected according to the temperature range of interest for aparticular unit. Again, the break points and coefficients for eachlinear approximation are stored in the EEPROM and are selected asrequired.

An additional factor based on ambient temperature may also be includedas an adjustment. The temperature of the ear T_(e) is sensed instead ofthe temperature of the tympanic membrane, the temperature sensed by thethermopile is not actually the core temperature T_(cr). There is thermalresistance between T_(cr) and T_(e). Further, there is thermalresistance between the sensed ear temperature and the ambienttemperature. The result is a sense temperature T_(e) which is a functionof the core temperature of interest and the ambient temperature. Basedon an assumed constant K_(C) which is a measure of the ratio of thermalresistances between T_(cr), T_(e) and T_(a), T_(cr) and T_(a) coretemperature can be computed as$T_{cr} = {T_{a} + \frac{T_{e} - T_{a}}{k_{c}}}$

This computation can account for a difference of from one-half to onedegree or more between core temperature and sensed ear temperature,depending on ambient temperature.

A similar compensation can be made in other applications. For example,in differential cutaneous temperature scanning, the significance of agiven differential reading may be ambient temperature dependent.

The actual computations performed by the processor are as follows,where:

H is the digital value of radiation signal presented to the processor

H_(o) is the electronic offset

Hc is corrected H (deg K⁴)

Tc is ambient and cold junction temperature (deg F)

Taf is 4th power of Tamb (deg K⁴)

Tt is target temperature (deg F)

Tz is ambient temp during cal (deg F)

Td is the displayed temperature

Rt is the thermistor signal

Kh is a radiation sensor gain cal factor

Zt is a thermistor zero cal factor

Th is the hot junction temperature

α_(ts) is the Seebeck coefficient of the thermopile at a specifiedtemperature

J is the number of junctions in the thermopile

Tco is a temperature coefficient for the Seebeck coefficient

Ts is the temperature at which α_(ts) is specified

Tcr is core temperature

kc is a constant for computing core temperature

V_(S) is the sensor output voltage

G_(FE) is the gain of the front end amplifier

K_(AD) is the analog-to-digital conversion factor

V_(S)=(H−H_(o))^(K)AD/GFE

Tc(deg F)=Thermistor lookup table (Rt)−Zt

T_(H)=[(Tco*T⁵+1)±[(Tco*Ts+1)²−(2*Tco)*[(Tco((Tc*Ts)−(TC²/2))+Tc+(V_(S)/J*α_(ts))]]^(½)]/Tco

Hc(deg K⁴)=Kh*(H−H_(o))*(1+Tco*((Th−Tc)/2−Tz))

Thf(deg K⁴)=4th power lookup table (Tc)

Tt(deg F)=(Hc+Thf)^(¼) (Final lookup table)

Tcr=Te+(Tt−Te)/kc

Tt(deg C)=(5/9)*(Tf(deg F)−32) optional

The following is a list of the information which may be contained in theEEPROM and therefore be programmable at the time of calibration:

Radiation sensor offset

Radiation sensor gain

Radiation sensor temperature coefficient

Thermistor offset

Ambient temperature at calibration

Thermistor lookup table

Final temperature lookup table

Adjustment factor F

Sound source functions:

Beep at button push in lock mode

none/20/40/80 milliseconds long

Beep at lock

none/20/40/80 milliseconds long

Beep at power down

none/20/40/80 milliseconds long

Beep at lowbattery

none/20/40/80 milliseconds long

interval 1/2/3 sec

single/double beep

Timeout functions:

Time to power-down

0.5 to 128 sec in 0.5 sec increments

Delay until lock

0.5 to 128 sec in 0.5 sec increments

Other functions:

Power-on button resets lock cycle

Power-on button resets peak detect

Display degrees C/degrees F

EEPROM “Calibrated” pattern to indicate that the device has beencalibrated

EEPROM checksum for a self-check by the processor

FIGS. 9A-9D provide a flowchart of the firmware stored in themicroprocessor 73. From reset when the instrument is turned on, thesystem is initialized at 110 and the contents of the EEPROM are readinto memory in the microprocessor at 112. At 114, the processor readsthe state of power and mode switches in the system. At 116, the systemdetermines whether a mode switch 113 has placed the system in aself-test mode. If not, all eights are displayed on the four-digitdisplay 82 for a brief time. At 120, the system performs all A-to-Dconversions to obtain digital representations of the thermopile outputand the potentiometer settings through multiplexor 76.

The system then enters a loop in which outputs dictated by the modeswitch are maintained. First the timers are updated at 122 and theswitches are again read at 124. When the power is switched off, from 126the system enters a power down loop at 128 until the system is fullydown. At 130, the mode switch is checked and if changed the system isreset. Although not in the tympanic temperature detector, some detectorshave a mode switch available to the user so that the mode of operationcan be changed within a loop.

At 132, 136 and 140, the system determines its mode of operation andenters the appropriate scan process 134, lock process 138 or peakprocess 142. In a scan process, the system updates the output to thecurrent reading in each loop. In a lock process, the system updates theoutput but locks onto an output after some period of time. In the peakprocess, the system output is the highest indication noted during ascan. In each of these processes, the system may respond to theprogramming from the EEPROM to perform any number of functions asdiscussed above. In the peak process which is selected for the tympanictemperature measurement, the system locks onto a peak measurement aftera preset period of time. During assembly, the system may be set at atest mode 144 which will be described with respect to FIG. 9D.

In any of the above-mentioned modes, an output is calculated at 146.Then the system loops back to step 122. The calculation 146 isillustrated in FIG. 9B.

At 148 in FIG. 9B, the raw sensor data is obtained from memory. Thesensor offset taken from the EEPROM is subtracted at 150, and theambient temperature previously obtained from the potentiometer RT1 isaccessed at 152. The temperature coefficient adjustment is calculated at154. At 156, the sensed signal is multiplied by the gain from EEPROM andby the temperature coefficient. At 158, the fourth power of the ambienttemperature is obtained, and at 160 it is added to the sensor signal. At162, the fourth root of the sum is obtained through a lookup table.Whether the display is in degrees centigrade or degrees Fahrenheit isdetermined at 164. If in degrees centigrade, a conversion is performedat 166. At 168, adjustment values, including that from the potentiometerR4, are added.

Analog-to-Digital conversion is performed periodically during aninterrupt to the loop of FIG. 9A which occurs every two milliseconds.The interrupt routine is illustrated in FIG. 9C. Timer counters areupdated at 170. A-to-D conversions are made from 172 only every 100milliseconds when a flag has been set in the prior interrupt cycle.During most interrupts, an A/D conversion does not occur. Then, the100-millisecond counter is checked at 174, and if the count has expired,a flag is set at 176 for the next interrupt. The flag is checked at 178and, if found, the display is updated at 180. The system then returns tothe main loop of FIG. 9A.

Where the 100 millisecond flag is noted at 172, an A-to-D conversion isto be performed. The system first determines at 182 whether a countindicates there should be a conversion of the thermopile output at 184or a conversion of the thermistor output at 186. The thermopile sensorconversion is performed nine out of ten cycles through the conversionloop. At 188, the system checks to determine whether a conversion ismade from the potentiometer R4 or from the battery voltage divider R1,R2 at 192. These conversions are made alternately.

FIG. 9D illustrates the self-test sequence which is called by the modeswitch 113 only during assembly. During the test, the beeper sounds at182 and all display segments are displayed at 184. Then the system stepseach character of the display from zero through nine at 186. The systemthen enters a test loop. At 188, the system senses whether the button108 has been pressed. If so, a display counter is incremented at 190.The display for the unit then depends on the count of the displaycounter. With the zero count, the adjustment potentiometer value isdisplayed at 192. Thereafter, if the display counter is incremented bypressing the button 108, the raw sensor data is displayed. With the nextincrement, ambient temperature is displayed at 196, and with the nextincrement, the raw output from the ambient temperature sensor RT1 isdisplayed. With the next increment, the battery voltage is displayed.After the test, the assembler sets the mode switch to the properoperating mode.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims. For example, most featuresof the invention may be applied to a device having a pyroelectricradiation sensor. Also certain features such as the low reflectance,high thermal conductivity tube may provide stable response and narrowfield of view even where the tube is thermally isolated from the sensor.In that case, a second temperature sensor would be provided for the tubeto compensate for temperature differences between the tube and sensorcold junction.

What is claimed is:
 1. A temperature detector comprising: a housingadapted to be held by hand; a radiation sensor in the housing; a tubefor directing radiation from a target to the radiation sensor, the tubehaving a rigid window at an end thereof away from the radiation sensor;a temperature display on the housing for displaying temperature of thetarget; and battery powered electronics in the housing for convertingradiation sensed by the sensor to temperature displayed by the display.